A known conventional technique for measuring wheel alignment of an automobile is described in Japanese Patent No. 2938984, for example. According to this technique, the toe angle and the camber angle of a wheel are measured via a wheel installation portion without fitting a wheel to the wheel installation portion in the automobile assembly line to enhance productivity.
According to the measurement method of this kind, in the automobile assembly line, a steering unit and a suspension unit are fitted onto an automobile body carried by a hanger, and then, the automobile body is separated from the hanger. At this time, a positioning pin provided below the automobile body supported by the hanger is fitted into a positioning hole of the automobile body, thereby positioning the automobile body. The automobile body is supported via a wheel installation portion, which is provided on the automobile body as a result of fitting of the suspension unit to the automobile body, in such a manner that the automobile body can be lifted and lowered. Then, lowering means is coupled to the front and the rear part of the automobile body via a linkage of the lowering means, such as a chain, and the automobile body is lowered to apply a predetermined load on the automobile body. Thus, a biasing force equivalent to the predetermine load is exerted on the suspension unit by the reaction force from the wheel installation portion, and the automobile body is settled in a state closest to the finished vehicle state in which wheels are fitted onto the axles. Then, while maintaining this state, the toe angle and the camber angle are measured via the wheel installation portion.
However, according to such a conventional method, the automobile has to be put in a state closest to the finished vehicle state, and the automobile separated from the hanger has to be positioned and pulled downward by the lowering means before measuring the toe angle and the camber angle. Thus, the method requires a relatively large number of measurement steps and is disadvantageously inefficient.
To overcome the disadvantage, it can be contemplated that the toe angle and the camber angle are measured on the automobile body supported by the hanger, instead of separating the automobile body from the hanger. In this case, the step of positioning the automobile body and the step of pulling downward the automobile body can be omitted, so that measurement can be conducted efficiently.
However, there is a play between the roller on the top of the hanger carrying the automobile and the carriage rail that guides the roller, and the center of gravity of the automobile body varies depending on the components mounted on the automobile body. Thus, an automobile body supported by a hanger may horizontally deviate from a predetermined orientation, or a hanger may be unable to support an automobile in a horizontal position, so that the automobile body may be inclined in a lateral direction. The toe angle and the camber angle measured on the automobile body supported by the hanger are disadvantageously inaccurate because of the inappropriate attitude of the automobile body at the time of measurement.
Furthermore, it is known that, if the suspension unit is a double-wishbone-type suspension, the toe angle is affected by the vertical distance between the mounting points of an upper arm and a lower arm or the displacement along the axle between the mounting points of the upper arm and the lower arm. Thus, it is desirable that the mounting states of the upper arm and the lower arm, which are components constituting the suspension unit, are grasped without putting the automobile in a state closest to the finished vehicle state as with the conventional method, and the result of measurement of wheel alignment is quickly reflected in the assembly step of the suspension unit.
The present invention eliminates such disadvantages, and an object of the present invention is to provide a method and a device for measuring wheel alignment of an automobile that can measure wheel alignment quickly and precisely without placing the same load on a wheel installation portion as that placed thereon in a finished vehicle state to improve the productivity and can quickly reflect the result of measurement of wheel alignment in an assembly process of a suspension unit.